Severe Weather SWBAT explain why some thunderstorms are more severe than others; recognize the dangers of severe thunderstorms; describe how tornadoes form

Severe Thunderstorms  Why are some thunderstorms more severe than other? An increased temperature difference between the upper and lower parts of the storm can cause the air to be more unstable. The greater the instability the more severe the storm is, due to the increased up and down drafts. An increased temperature difference between the upper and lower parts of the storm can cause the air to be more unstable. The greater the instability the more severe the storm is, due to the increased up and down drafts.

Severe Thunderstorms  Supercell Self-sustaining, extremely powerful storms that are characterized by intense, rotating updrafts Self-sustaining, extremely powerful storms that are characterized by intense, rotating updrafts

Dangers Associated with Thunderstorms  Lightning Electricity caused by the rapid rush of air in a cumulonimbus cloud. Electricity caused by the rapid rush of air in a cumulonimbus cloud. A bolt forms when friction between the updrafts and downdrafts separate electrons from some of the atoms creating positively charged ions and regions of opposite charge. A bolt forms when friction between the updrafts and downdrafts separate electrons from some of the atoms creating positively charged ions and regions of opposite charge. To relieve the imbalance a channel of negatively charged air moves from the cloud to the ground causing a positively charged ion channel to surge back up from the ground, channeling about 100 million volts of electricity. To relieve the imbalance a channel of negatively charged air moves from the cloud to the ground causing a positively charged ion channel to surge back up from the ground, channeling about 100 million volts of electricity.

Dangers Associated with Thunderstorms  Wind Sometimes the downdrafts are not dispersed and are concentrated in downbursts. Sometimes the downdrafts are not dispersed and are concentrated in downbursts. They travel between 200 and 250 km/hr (approximately mph) and can be deadly even though they don’t last long. They travel between 200 and 250 km/hr (approximately mph) and can be deadly even though they don’t last long.

Dangers Associated with Thunderstorms  Hail Precipitation in the form of lumps of ice. Precipitation in the form of lumps of ice. It can cause tremendous damage (almost $1 billion a year). It can cause tremendous damage (almost $1 billion a year). It’s most common during the spring. It’s most common during the spring. If caught in a convection current hail can grow quite large before they fall. If caught in a convection current hail can grow quite large before they fall.

Dangers Associated with Thunderstorms  Floods Slower moving storms dump more rain over a limited location, rather than spreading it out. Slower moving storms dump more rain over a limited location, rather than spreading it out. If there is abundant moisture in the area it is easier to cause flooding. If there is abundant moisture in the area it is easier to cause flooding. Floods are the main cause of thunderstorms related deaths in the US each year. Floods are the main cause of thunderstorms related deaths in the US each year.

Dangers Associated with Thunderstorms  Tornados Violent, whirling column of air in contact with the ground (funnel cloud). Violent, whirling column of air in contact with the ground (funnel cloud). These are associated with the most severe thunderstorms. These are associated with the most severe thunderstorms. They form when wind speed and direction change suddenly with height, known as a wind shear. They form when wind speed and direction change suddenly with height, known as a wind shear. If the rotation takes place near an updraft it can tilted vertically. If the rotation takes place near an updraft it can tilted vertically.

Severe Weather  Downbursts Violent downdrafts that are concentrated in a local area Violent downdrafts that are concentrated in a local area  Fujita tornado intensity scale A rank is given according to a tornados path of destruction, wind speed, and duration A rank is given according to a tornados path of destruction, wind speed, and duration

With a partner  Answer assessment questions 1-6, on page 340  Be sure to answer in complete sentences.  Finish for homework.